Final answer:
The molecular geometry is tetrahedral when a central atom has four single bonds and no lone pairs.
Step-by-step explanation:
The molecular geometry of a molecule with a central atom that has four single bonds is tetrahedral. When there are four electron groups around the central atom, these electron groups are oriented in the direction of a tetrahedron. If all four groups are bonded to other atoms, with no lone pairs of electrons on the central atom, the molecular shape mirrors the electron-pair geometry and is also tetrahedral. An example of such a molecule is methane (CH4), where the carbon atom is at the center and the four hydrogen atoms are at the corners of the theoretical tetrahedron, creating bond angles of approximately 109.5° between them.